Field of the Invention
The present disclosure relates to a driving device of a rotating polygonal mirror for driving a rotating polygonal mirror including a plurality of reflection surfaces, and an image forming apparatus including the driving device.
Description of the Related Art
An image forming apparatus has been known, which deflects a light beam emitted from a light source by using a rotating polygonal mirror (hereinafter, polygonal mirror) including a plurality of reflection surfaces so that the deflected light beam scans a photosensitive member to form an electrostatic latent image on the photosensitive member. Characteristics of the polygonal mirror such as reflectance of each reflection surface and an angle (plane tilt) thereof with respect to the rotation axis vary depending on cutting accuracy during manufacturing. Variations in the manufacturing accuracy therefore need to be corrected by identifying the reflection surface on which the light beam is incident and making corrections according to the identified reflection surface.
As a method for identifying the reflection surface on which the light beam is incident, Japanese Patent Application Laid-Open No. 2007-78723 discloses an image forming apparatus that identifies the reflection surface on which the light beam is incident by using a beam detecting (BD) signal and a frequency generator (FG) signal. The BD signal is generated by a BD (Beam Detector) that receives the light beam deflected by each of the plurality of reflection surfaces during one rotation. The FG signal is generated by detecting a magnetic pattern arranged on a driving motor that rotates the polygonal mirror.
Since the FG signal is generated by detecting the magnetic pattern, the FG signal (generally sinusoidal curves 1201 and 1203 in FIG. 12) includes noise 1203 generated due to the influence of a driving current supplied to a coil of the driving motor. This can make it difficult to accurately detect the period of the FG signal.